The present invention relates to a color-picture tube and to a method of manufacturing the color-picture tube.
U.S. Pat. No. 4,031,597 discloses a color-picture tube having a conductive coating on the inside of the cone. The coating is made of graphite, iron oxide, and a silicate binder. The entire inside of the neck of the color-picture tube is coated with a film of vaporizable material, e.g., polyvinyl alcohol. This film serves to protect the neck during the insertion of the electron-gun system. After the electron-gun system has been mounted, the film in the neck is vaporized.
To avoid sparkover between the conductive coating in the cone, which is at high electric potential, and the electron-gun system, there must be a sharp boundary between the conductive coating and the uncoated area. The thickness of the coating must be very uniform, and the boundary region between the coated and uncoated areas must be very smooth, because otherwise material of the coating would easily crumble away at bulging transitions, particularly when the centering and contact springs of the electron-gun system are moved over the boundary.
DE-OS No. 29 03 735 discloses a method of applying a conductive coating to the cone of a color-picture tube which comprises the steps of covering the areas which are to remain free of the coating with a lacquer film, then depositing the conductive coating, and finally washing away the lacquer film and the conductive coating resting on the film.